Essay on Microorganisms | Microbiology

In this essay we will discuss about Microorganisms. After reading this essay you will learn about: 1. Hidden World of Microorganisms 2. General Classification of Microorganisms 3. Importance in Human Welfare.

Contents:

1. Essay on the Hidden World of Microorganisms
2. Essay on the General Classification of Microorganisms
3. Essay on the Importance of Microorganisms in Human Welfare

Essay # 1. The Hidden World of Microorganisms:

The microorganisms are very minute in size and constitute the vast and diverse microbial world which occupies every nook and cranny of the Earth, from the deepest depths of the ocean to the highest mountain peaks, living in the water, soil, and air that surrounds us, on and in the food that we eat, on and within our bodies.

Nominal cell counts of > 10⁵ cells per ml in surface sea water predict that the oceans harbour 3.6 x 10²⁶ microbial cells.

Communities of bacteria, archaea, microalgae, protozoans, and micro fungi account for most of the oceanic biomass. These microscopic factories are responsible for 98% of primary production and mediate all biogeochemical cycles in the oceans.

Estimates proclaim that there are more bacterial cells in our body than human cells, for convenience, there are 10¹⁴ microorganisms in our colon and trillions more on our hands and in our mouth.

Whitman and his colleagues have given an analysis in 1998 exploring the abundance of prokaryotes. This analysis suggested that the total number of living prokaryotic cells is 4-6 x 10³⁰ composed of 1.2 x 10²⁹ cells in ocean, 2.6 x 10²⁹cells in soil, and 0.25-2.4 x 10³⁰ cells within the earths subsurface.

An alternative way to appreciate these figures is that even while accounting for the idea that a prokaryotic cells is typically about 10,000-fold smaller in volume than a eukaryotic cells, the total amount of prokaryote biomass is still approximately 10,000 times greater than the amount of human biomass currently present on Earth.

Despite the fact that microorganisms comprise most of the Earth’s biomass, maintain its environment, and hold the key both to understanding the history and health of life on Earth and to exploiting the full potential of biotechnology for myriad applications, with some notable exceptions, we still know almost nothing about most of them.

A comparison of the numbers of described species of microorganisms to the estimated numbers highlights the fact that the current description constitutes an almost insignificant number in terms of the inventory of all species currently residing on Earth (Table 1.1).

Now, with the advent of genomics (the study of an organism’s entire DNA complement and its function), we are entering a new era of scientific discovery that holds good promise for understanding the complexity of the microbial world.

2. General Classification of Microorganisms:

We all know that there are tremendous number of microorganisms on the earth. They are ubiquitous in occurrence, have plasticity in their genome, possess adaptability to varying conditions of environment, enjoy specialties in their life-style and biochemistry, and represent diversity in their mode of nutrition. Therefore, the microorganisms can be classified in different categories from different viewpoints.

The classification of microorganisms can be given as under:

1. On the Basis of their Body and Nuclear Organization:

Microorganisms can be classified into two categories on the basis of their body organization:

(i) Microbes beyond cellular-organization,

(ii) Cellular microorganisms.

Microbes beyond cellular organization, in spite of having the characters of cellular organisms, are completely devoid of any cell structure in their body organization, e.g., viruses, viroids, prions, and virusoids. Contrary to it, the cellular microorganisms have their body made up of cells, e.g., bacteria, microalgae, micro fungi, protozoans, etc.

On the basis of nuclear organization the cellular microbes can further be grouped into two:

(i) Prokaryotes,

(ii) Eukaryotes.

Prokaryotic microorganisms are those that possess incipient nucleus that lacks nuclear membrane, nucleoplasm and nucleolus (archaebacteria, cyanobacteria and eubacteria). In contrast, the eukaryotic microorganisms possess a well-developed nucleus with nuclear membrane, nucleoplasm and nucleolus (microalgae, protozoans, slime moulds and micro fungi).

2. On the Basis of Organisms’ Classification:

Whittaker’s (1969) five kingdom system of organisms’ classification categorizes all organisms into five different kingdoms, namely, Monera, Protista, Mycophyta, Plantae, and Animalia. The microorganisms (except viruses, viroids, etc.) are grouped in three of them. The bacteria and cyanobacteria are monerans; microalgae, protozoans and slime moulds are protistans and; the micro fungi are mycophytans.

Woese’s domain-system consists of three domains of life, namely, Bacteria, Archaea, and Eukarya. Bacteria and cyanobacteria belong to domain Bacteria, arcbhacbacteria to domain Archaea, and all eukaryotic microorganisms (microalgae, protozoa, slime moulds, fungi) belong to domain Eukarya.

3. On the Basis of Nutrition:

Microorganisms can be classified into four categories on the basis of their mode of nutrition.

These categories are:

(i) Photoautotrophs,

(ii) Chemoautotrophs,

(iii) Photoheterotrophs, and

(iv) Chemoheterotrophs.

Photoautotrophs are those that use light-energy to manufacture (synthesize) their food; photosynthetic microalgae, cyanobacteria, and photosynthetic bacteria are the examples. Chemoautotrophs are those that use chemical-energy to manufacture their food; the group consists only of bacteria like sulphur bacteria, iron bacteria, nitrifying bacteria, etc.

Photoheterotrophs are the microorganisms that use light-energy in obtainment (absorption) of their food from external environment; purple non-sulphur bacteria are examples. Chemoheterotrophs (saprophytic bacteria, symbiotic bacteria, micro fungi, protozoa, and colourless microalgae) are those that use chemical-energy in obtainment (absorption) of their food from external environment.

4. On the Basis of Oxygen Requirements:

Microorganisms can be classified on the basis of their requirements of oxygen as:

(i) Obligate aerobes (need molecular oxygen),

(ii) Obligate anaerobes (grow in absence of oxygen),

(iii) Facultative anaerobes (aerobes having ability to grow in absence of oxygen), and

(iv) Facultative aerobes (anaerobes that can grow even in the presence of oxygen).

5. On the Basis of Temperature Requirements:

Microbial growth is affected by temperature of the environment to a great degree. In this respect, the microorganisms can be classified as under.

(i) Psychrophilic or Cryophilic:

Require sufficiently low temperature for their survival. Their best growth occurs at 0°C temperature as the minimum, 15-20°C as optimum, and 30°C as maximum.

(ii) Mesophilic:

Grow on moderate temperature; minimum, optimum, and maximum temperature limits are 15-25°C, 25-40°C and 50°C, respectively.

(iii) Thermophilic:

Grow at elevated temperatures lethal to many others. Their minimum temperature limit is 25-45°C, optimum as 45-55°C, and maximum limit is 55-85°C.

(iv) Thermotolerants or Thermoduric:

Certain mesophilic microorganisms are capable of withstanding high temperature, though they do not multiply at these elevated temperatures.

(v) Psychro- or Cryotolerants:

They are also called psychroduric or cryoduric. These are those mesophilic microorganisms that can survive at very low temperatures but do not grow and multiply.

6. On the Basis of Distribution:

On the basis of their distribution in environment, the microorganisms can be classified into three categories:

(i) Hydrospheric or aquatic (microorganisms that grow in water),

(ii) Lithospheric or terrestrial (microorganisms that grow on or in soil or rocky-substances), and

(iii) Atmospheric or aerial (microorganisms that are found in atmosphere; atmosphere being their being temporary abode as they cannot grow and multiply in air in absence of adequate moisture and nutrients).

7. On the Basis of Osmotic Conditions:

Osmotic concentrations of substrates where upon the microorganisms grow help classifying them as under:

(i) Osmophobic microorganisms that die of dehydration if subjected to substrates of high osmotic concentrations),

(ii) Osmophilic (microorganism that best grown on substrates of high osmotic concentrations),

(iii) Halophilic. (microbes that preferably grow in high osmotic concentrations produced by dissolved salts), and

(iv) Osmoduric (microorganisms that grow normally on substrates of moderate osmotic concentrations but prove to be resistant to wide osmotic changes in their substratum).

Essay # 3. Importance of Microorganisms in Human Welfare:

Microbiology is as an area of activity having a marked realized as well as potential impact on virtually all domains of human welfare, ranging from food processing, protecting the environment, to human health. As a result, it now plays a very important role in the employment, production and productivity, trade, economics and economy, human health, and the quality of human life throughout the world.

This is clearly reflected in the emergence of numerous companies throughout the world, including India, and the movement of noted scientists, including Nobel Laureates, to some of these companies.

The total volume of trade in microbiological products is increasing sharply every year, and it is expected to soon become the major contributor to world trade. Many commentators are confident that the 21st century will be the century of microbial biotechnology, just as the 20th century is the era of electronics.

The importance of microorganisms in human welfare would become obvious from some selected examples given as follows:

(i) Human Health:

Infectious disease caused by microorganisms have been of mankind for centuries and continue to cause highly morbidity and sufferings worldwide. Disease and death have always attracted the attention of the human mind.

The emergence of acquired immunodeficiency syndrome (AIDS) caused by human immunodeficiency virus (HIV) as a major modern day scourge with tremendous public health importance has brought into limelight even those diseases which were considered rare in the past. Applications of microbiology have given medicine the greatest success in the diagnosis prevention, and cure of disease (Table 1.2).

Production of variety of antibiotics, e.g., penicillin, streptomycin, erythromycin, cyclohexamide, etc. by fungi, bacteria and actinomycetes as secondary metabolites and their significant role in controlling microbial diseases is well known to each of us.

(ii) Food:

1. Dairy Products, Baked Goods, and Alcohol:

Many dairy products are manufactured, at least in part, via microbial activity. They include cheese, yogurt, buttermilk, etc. and are of major economic value. Similarly, sauerkrant, pickles and some sausages also owe their existence to microbial activity. Baked goods (e.g., breads, etc.) are made using yeasts. Even more pervasive in our society are alcoholic beverages which are also based on the activities of yeasts.

2. Food Canning:

We know that food spoilage by variety of microorganisms results in immense economic loss every year. The canning, frozen-food, and dried food industries exist to prepare food in such ways that they will not undergo microbial spoilage.

3. Single Cell Protein (SCP):

Some microorganisms have long been used as human food, e.g., the blue- green alga Spirulina and the fungi commonly known as mushrooms. More recently, efforts have been made to produce microbial biomass using low cost substrates and use it for human consumption. Since this microbial biomass is rich in protein, it is popularly called single cell protein (SCP). SCP can be produced using algae, fungi, yeasts and bacteria.

The substrates used for SCP production range from CO₂ (used by algae) through industry effluents like whey, etc. to low cost organic materials like saw dust and paddy straw.

Commercial production of SCP is mostly based on yeasts and some other fungi, including mushrooms. In most cases, SCP has to be processed to remove the excess of nucleic acids. SCP is rich in high quality protein and is rather poor in fats. Both these features are desirable in human food.

SCP provides a valuable protein-rich supplement in human diet. Their use should help bridge the gap between the requirement and the supply of proteins in human diet. It should also reduce the pressure on agricultural production systems for the supply of the required proteins. In addition, SCP production based on industrial effluents helps reduce environmental pollution.

(iii) Agriculture:

1. Biological N₂-Fixation:

A number of major crops are members of a plant group called legumes, which live in close association with specific bacteria that form structures called nodules on their roots. In these root nodules, atmospheric N₂ is converted to fixed nitrogen compounds that the plants can use for growth. In this way, the activities of the root nodule bacteria (Rhizobium spp.) reduce the need for costly plant fertilizer.

2. Biogeochemical Cycles:

Microorganisms also play master roles in the cycling of important nutrients in plant nutrition, particularly, carbon, nitrogen and sulphur. Microbial activities in soil and water convert these elements to forms that are readily accessible to plants.

3. Biofertilizers:

Microorganisms employed to enhance the availability of nutrients like nitrogen (N), and phosphors (P) crops are called biofertilizers. Several microorganisms, e.g.. bacteria and cyanobacteria (blue- green alage), fix atmospheric nitrogen and make them available to plants.

For example rhizobia from root nodules in legume crops like pulses. Similarly, phosphate is solubilized by some bacteria and by some fungi that form association with plant roots called mycorrhiza. Several other mircoorganisms used as biofertilizer promote plant growth and protect plants from soil pathogens.

Bio-fertilizers are a low cost input and they do not pollute the environment. They also reduce the dependence on chemical fertilizers that are produced from non-renewable natural resources and pollute the environment. Therefore, extensive efforts are being made to enhance the effectiveness and the contribution of bio-fertilizers to agricultural production.

4. Bio-pesticides:

Bio-pesticides are those biological agents that are used for control of weeds, insects, and pathogens. The micro-organisms used as bio-pesticides include viruses, bacteria, fungi, protozoa and mites. Some of the bio-pesticides are being used even at a commercial scale.

Insects are attacked by many microorganisms as well as mites. Of these, certain viruses, bacteria and fungi are used at commercial scale. One example is the soil bacterium Bacillus thuringiensis. Spores of this bacterium produce an insecticidal crystal protein.

Therefore, spores of this bacterium kill larvae of certain insects. The commercial preparations of B. theringiensis contain a mixture of spores, crystal protein and an inert carrier.

This bacterium was the first biopesticide to be used on a commercial scale and is also likely to become the first such product to be produced at commercial scale in India. Certain bacteria and fungi are also being used for the control of some weeds and diseases in various crops.

The use of bio-pesticides is expected to reduce the application of chemicals for control of diseases, insect pests and weeds. These chemicals are a source of widespread pollution. In addition, the presence of their residues in agricultural products is hazardous to human health.

(iv) Management of Environmental Pollution:

Humans have strived to minimise the damaging effects of their activities causing environmental pollution in the following two ways:

(1) Development of “cleaner” production technologies that generates less pollution (these are called front-of-the pipe technologies), and

(2) Devising of such methods and strategies that clean up the pollution generated by the various human activities (these are termed as end-of-the pipe technologies).

Microbial biotechnology has immense potential of contribution to both the above strategies. Bioremediation strategies aim at cleaning up pollutants. Various microorganisms have now been isolated from nature that consume spilled oil, solvents, pesticides, and other environmentally toxic pollutants, either directly at the site of the spill or later on after the toxic materials have pervaded soils and entered the ground water.

Other example is the production of biodegradable plastic from polyhydroxybutyrate, which is currently obtained from bacterial fermentation. Attempts are being made to produce this biopolymer in transgenic plants; this is expected to reduce cost and increase the supply of biodegradable plastic. This would greatly reduce the menace to the environment posed by the non-biodegradable plastic now in common use.

(v) Energy Production:

When it comes to energy, microorganisms play major roles. Most natural gas (methane) is a product of bacterial action, arising from the activities of methanogenic archaebacteria. Phototrophic microorganisms can harvest light energy for the production of biomass, energy stored in living organisms. Microbial biomass and existing waste materials such as domestic refuse, animal wastes, etc. can be converted to biofuels (e.g., methane, ethanol) by the degradative activities of microorganisms.

(vi) Metal Extraction (Biomining):

Some microorganisms are used in extracting valuable metals like uranium, copper, iron, etc. through leaching from low greed ores. For example, Thiobacillus bacteria are used in mining operation of iron ore.